From 89f7e23b29936eaf84df199d1951b0abc819ba17 Mon Sep 17 00:00:00 2001
From: soronpo <oron.port@cornell.edu>
Date: Tue, 21 Sep 2021 21:31:52 -0400
Subject: [PATCH] Add SkolemType in metaprogramming

---
 .../scala/quoted/runtime/impl/QuotesImpl.scala   | 12 ++++++++++++
 .../runtime/impl/printers/Extractors.scala       |  2 ++
 .../runtime/impl/printers/SourceCode.scala       |  5 +++++
 library/src/scala/quoted/Quotes.scala            | 16 ++++++++++++++++
 4 files changed, 35 insertions(+)

diff --git a/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala b/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala
index 80c6dc757aaa..a51ac42a1f66 100644
--- a/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala
+++ b/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala
@@ -2216,6 +2216,18 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
       def unapply(x: NoPrefix): true = true
     end NoPrefix
 
+    type SkolemType = dotc.core.Types.SkolemType
+
+    object SkolemTypeTypeTest extends TypeTest[TypeRepr, SkolemType]:
+      def unapply(x: TypeRepr): Option[SkolemType & x.type] = x match
+        case tpe: (Types.SkolemType & x.type) => Some(tpe)
+        case _ => None
+    end SkolemTypeTypeTest
+
+    object SkolemType extends SkolemTypeModule:
+      def unapply(x : SkolemType) : Some[TypeRepr] = Some(x.info)
+    end SkolemType
+
     type Constant = dotc.core.Constants.Constant
 
     object Constant extends ConstantModule
diff --git a/compiler/src/scala/quoted/runtime/impl/printers/Extractors.scala b/compiler/src/scala/quoted/runtime/impl/printers/Extractors.scala
index 0bea8f0ab643..eb0fe2f5ee03 100644
--- a/compiler/src/scala/quoted/runtime/impl/printers/Extractors.scala
+++ b/compiler/src/scala/quoted/runtime/impl/printers/Extractors.scala
@@ -240,6 +240,8 @@ object Extractors {
         this += "NoPrefix()"
       case MatchCase(pat, rhs) =>
         this += "MatchCase(" += pat += ", " += rhs += ")"
+      case SkolemType(info) =>
+        this += "SkolemType(" += info += ")"
     }
 
     def visitSignature(sig: Signature): this.type = {
diff --git a/compiler/src/scala/quoted/runtime/impl/printers/SourceCode.scala b/compiler/src/scala/quoted/runtime/impl/printers/SourceCode.scala
index 77a54e23ad61..444adff782e4 100644
--- a/compiler/src/scala/quoted/runtime/impl/printers/SourceCode.scala
+++ b/compiler/src/scala/quoted/runtime/impl/printers/SourceCode.scala
@@ -1234,6 +1234,11 @@ object SourceCode {
         this += " => "
         printType(rhs)
 
+      case SkolemType(info) =>
+        this += "$skolem["
+        printType(info)
+        this += "]"
+
       case _ =>
         throw new MatchError(tpe.show(using Printer.TypeReprStructure))
     }
diff --git a/library/src/scala/quoted/Quotes.scala b/library/src/scala/quoted/Quotes.scala
index a1199fc42169..b1da7bbe2b67 100644
--- a/library/src/scala/quoted/Quotes.scala
+++ b/library/src/scala/quoted/Quotes.scala
@@ -3163,6 +3163,22 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
       def unapply(x: NoPrefix): true
     }
 
+    // ----- SkolemType -----------------------------------------------
+
+    /** SkolemType for a type selection */
+    type SkolemType <: TypeRepr
+
+    /** `TypeTest` that allows testing at runtime in a pattern match if a `TypeRepr` is a `SkolemType` */
+    given SkolemTypeTypeTest: TypeTest[TypeRepr, SkolemType]
+
+    /** Module object of `type SkolemType`  */
+    val SkolemType: SkolemTypeModule
+
+    /** Methods of the module object `val SkolemType` */
+    trait SkolemTypeModule { this: SkolemType.type =>
+      def unapply(x: SkolemType): Some[TypeRepr]
+    }
+
     ///////////////
     // CONSTANTS //
     ///////////////